Koine Greek: The fusion of Ionian with Attic, the dialect of Athens, began the process that resulted in the creation of the first common Greek dialect, which became a lingua franca across the Eastern Mediterranean and Near East. Koine Greek can be initially traced within the armies and conquered territories of Alexander the Great and after the Hellenistic colonisation of the known world, it was spoken from Egypt to the fringes of India. After the Roman conquest of Greece, an unofficial bilingualism of Greek and Latin was established in the city of Rome and Koine Greek became a first or second language in the Roman Empire. The origin of Christianity can also be traced through Koine Greek, because the Apostles used this form of the language to spread Christianity. It is also known as Hellenistic Greek, New Testament Greek, and sometimes Biblical Greek because it was the original language of the New Testament and the Old Testament was translated into the same language via the Septuagint.

Medieval Greek, also known as Byzantine Greek: the continuation of Koine Greek in Byzantine Greece, up to the demise of the Byzantine Empire in the 15th century. Medieval Greek is a cover phrase for a whole continuum of different speech and writing styles, ranging from vernacular continuations of spoken Koine that were already approaching Modern Greek in many respects, to highly learned forms imitating classical Attic. Much of the written Greek that was used as the official language of the Byzantine Empire was an eclectic middle-ground variety based on the tradition of written Koine.

Modern Greek (Neo-Hellenic):[៧] Stemming from Medieval Greek, Modern Greek usages can be traced in the Byzantine period, as early as the 11th century. It is the language used by the modern Greeks, and, apart from Standard Modern Greek, there are several dialects of it.

In the modern era, the Greek language entered a state of diglossia: the coexistence of vernacular and archaizing written forms of the language. What came to be known as the Greek language question was a polarization between two competing varieties of Modern Greek: Dimotiki, the vernacular form of Modern Greek proper, and Katharevousa, meaning 'purified', a compromise between Dimotiki and Ancient Greek, which was developed in the early 19th century and was used for literary and official purposes in the newly formed Greek state. In 1976, Dimotiki was declared the official language of Greece, having incorporated features of Katharevousa and giving birth to Standard Modern Greek, which is used today for all official purposes and in education.

The historical unity and continuing identity between the various stages of the Greek language is often emphasised. Although Greek has undergone morphological and phonological changes comparable to those seen in other languages, never since classical antiquity has its cultural, literary, and orthographic tradition been interrupted to the extent that one can speak of a new language emerging. Greek speakers today still tend to regard literary works of ancient Greek as part of their own rather than a foreign language.[៨] It is also often stated that the historical changes have been relatively slight compared with some other languages. According to one estimation, "Homeric Greek is probably closer to demotic than 12-century Middle English is to modern spoken English."[៩]

The phonology, morphology, syntax and vocabulary of the language show both conservative and innovative tendencies across the entire attestation of the language from the ancient to the modern period. The division into conventional periods is, as with all such periodisations, relatively arbitrary, especially because at all periods, Ancient Greek has enjoyed high prestige, and the literate borrowed heavily from it.

Across its history, the syllabic structure of Greek has varied little: Greek shows a mixed syllable structure, permitting complex syllabic onsets but very restricted codas. It has only oral vowels and a fairly stable set of consonantal contrasts. The main phonological changes occurred during the Hellenistic and Roman period (see Koine Greek phonology for details):

simplification of the system of vowels and diphthongs: loss of vowel length distinction, monophthongisation of most diphthongs and several steps in a chain shift of vowels towards /i/ (iotacism).

development of the voicelessaspiratedplosives/pʰ/ and /tʰ/ to the voiceless fricatives/f/ and /θ/, respectively; the similar development of /kʰ/ to /x/ may have taken place later (the phonological changes are not reflected in the orthography, and both earlier and later phonemes are written with φ, θ, and χ).

development of the voiced plosives /b/, /d/, and /ɡ/ to their voiced fricative counterparts /β/ (later /v/), /ð/, and /ɣ/.

In all its stages, the morphology of Greek shows an extensive set of productive derivational affixes, a limited but productive system of compounding[១៥] and a rich inflectional system. Although its morphological categories have been fairly stable over time, morphological changes are present throughout, particularly in the nominal and verbal systems. The major change in the nominal morphology since the classical stage was the disuse of the dative case (its functions being largely taken over by the genitive). The verbal system has lost the infinitive, the synthetically-formed future and perfect tenses and the optative mood. Many have been replaced by periphrastic (analytical) forms.

Pronouns show distinctions in person (1st, 2nd, and 3rd), number (singular, dual, and plural in the ancient language; singular and plural alone in later stages), and gender (masculine, feminine, and neuter) and decline for case (from six cases in the earliest forms attested to four in the modern language).[១៦] Nouns, articles and adjectives show all the distinctions except for person. Both attributive and predicative adjectives agree with the noun.

The inflectional categories of the Greek verb have likewise remained largely the same over the course of the language's history but with significant changes in the number of distinctions within each category and their morphological expression. Greek verbs have synthetic inflectional forms for:

Many aspects of the syntax of Greek have remained constant: verbs agree with their subject only, the use of the surviving cases is largely intact (nominative for subjects and predicates, accusative for objects of most verbs and many prepositions, genitive for possessors), articles precede nouns, adpositions are largely prepositional, relative clauses follow the noun they modify and relative pronouns are clause-initial. However, the morphological changes also have their counterparts in the syntax, and there are also significant differences between the syntax of the ancient and that of the modern form of the language. Ancient Greek made great use of participial constructions and of constructions involving the infinitive, and the modern variety lacks the infinitive entirely (instead having a raft of new periphrastic constructions) and uses participles more restrictively. The loss of the dative led to a rise of prepositional indirect objects (and the use of the genitive to directly mark these as well). Ancient Greek tended to be verb-final, but neutral word order in the modern language is VSO or SVO.

Greek is a language distinguished by an extensive vocabulary. Most of the vocabulary of Ancient Greek was inherited, but it includes a number of borrowings from the languages of the populations that inhabited Greece before the arrival of Proto-Greeks.[១៨] Words of non-Indo-European origin can be traced into Greek from as early as Mycenaean times; they include a large number of Greek toponyms. The vast majority of Modern Greek vocabulary is directly inherited from Ancient Greek, but in some cases, words have changed meanings. Loanwords (words of foreign origin) have entered the language mainly from Latin, Venetian and Turkish. During the older periods of Greek, loanwords into Greek acquired Greek inflections, thus leaving only a foreign root word. Modern borrowings (from the 20th century on), especially from French and English, are typically not inflected.

Greek is an independent branch of the Indo-Europeanlanguage family. The ancient language most closely related to it may be ancient Macedonian,[២០] which many scholars suggest may have been a dialect of Greek itself, but it is so poorly attested that it is difficult to conclude anything about it.[២១] Independently of the Macedonian question, some scholars have grouped Greek into Graeco-Phrygian, as Greek and the extinct Phrygian share features that are not found in other Indo-European languages.[២២] Among living languages, some Indo-Europeanists suggest that Greek may be most closely related to Armenian (see Graeco-Armenian) or the Indo-Iranian languages (see Graeco-Aryan), but little definitive evidence has been found for grouping the living branches of the family.[២៣] In addition, Albanian has also been considered somewhat related to Greek and Armenian by some linguists. If proven and recognised, the three languages would form a new Balkan sub-branch with other dead European languages.[២៤]

Linear B, attested as early as the late 15th century BC, was the first script used to write Greek. It is basically a syllabary, which was finally deciphered by Michael Ventris and John Chadwick in the 1950s (its precursor, Linear A, has not been deciphered to this day). The language of the Linear B texts, Mycenaean Greek, is the earliest known form of Greek.

Another similar system used to write the Greek language was the Cypriot syllabary (also a descendant of Linear A via the intermediate Cypro-Minoan syllabary), which is closely related to Linear B but uses somewhat different syllabic conventions to represent phoneme sequences. The Cypriot syllabary is attested in Cyprus from the 11th century BC until its gradual abandonment in the late Classical period, in favor of the standard Greek alphabet.

Greek has been written in the Greek alphabet since approximately the 9th century BC. It was created by modifying the Phoenician alphabet, with the innovation of adopting certain letters to represent the vowels. The variant of the alphabet in use today is essentially the late Ionic variant, introduced for writing classical Attic in 403 BC. In classical Greek, as in classical Latin, only upper-case letters existed. The lower-case Greek letters were developed much later by medieval scribes to permit a faster, more convenient cursive writing style with the use of ink and quill.

The Greek alphabet consists of 24 letters, each with an uppercase (majuscule) and lowercase (minuscule) form. The letter sigma has an additional lowercase form (ς) used in the final position:

In addition to the letters, the Greek alphabet features a number of diacritical signs: three different accent marks (acute, grave, and circumflex), originally denoting different shapes of pitch accent on the stressed vowel; the so-called breathing marks (rough and smooth breathing), originally used to signal presence or absence of word-initial /h/; and the diaeresis, used to mark full syllabic value of a vowel that would otherwise be read as part of a diphthong. These marks were introduced during the course of the Hellenistic period. Actual usage of the grave in handwriting saw a rapid decline in favor of uniform usage of the acute during the late 20th century, and it has only been retained in typography.

After the writing reform of 1982, most diacritics are no longer used. Since then, Greek has been written mostly in the simplified monotonic orthography (or monotonic system), which employs only the acute accent and the diaeresis. The traditional system, now called the polytonic orthography (or polytonic system), is still used internationally for the writing of Ancient Greek.

In Greek, the question mark is written as the English semicolon, while the functions of the colon and semicolon are performed by a raised point (•), known as the ano teleia (άνω τελεία). In Greek the comma also functions as a silent letter in a handful of Greek words, principally distinguishing ό,τι (ó,ti, "whatever") from ότι (óti, "that").[២៥]

Greek has occasionally been written in the Latin script, especially in areas under Venetian rule or by Greek Catholics. The term Frankolevantinika / Φραγκολεβαντίνικα applies when the Latin script is used to write Greek in the cultural ambit of Catholicism (because Frankos / Φράγκος is an older Greek term for Roman Catholic). Frankochiotika / Φραγκοχιώτικα (meaning "Catholic Chiot") alludes to the significant presence of Catholic missionaries based on the island of Chios. Additionally the term Greeklish is often used when the Greek language is written in a Latin script in online communications.[២៦]

↑The four cases that are found in all stages of Greek are the nominative, genitive, accusative and vocative. The dative/locative of Ancient Greek disappeared in the late Hellenistic period, and the instrumental case of Mycenaean Greek disappeared in the Archaic period.

↑There is no particular morphological form that can be identified as 'subjunctive' in the modern language, but the term is sometimes encountered in descriptions even if the most complete modern grammar (Holton et al. 1997) does not use it and calls certain traditionally-'subjunctive' forms 'dependent'. Most Greek linguists advocate abandoning the traditional terminology (Anna Roussou and Tasos Tsangalidis 2009, in Meletes gia tin Elliniki Glossa, Thessaloniki, Anastasia Giannakidou 2009 "Temporal semantics and polarity: The dependency of the subjunctive revisited", Lingua); see Modern Greek grammar for explanation.